1. Technical Field
The present invention relates to a laser light source device including a laser light source that emits a laser beam and an illumination apparatus, a monitor, and a projector including the laser light source device.
2. Related Art
A second harmonic generation (SHG) technique for generating light having a wavelength half that of incident light is well known as a technique for wavelength conversion. It is possible to obtain a laser beam having a wavelength in a visible region using an easily available semiconductor laser, which oscillates in a far infrared region, by combining this SHG technique with a semiconductor laser technique.
An example of the technique obtained by combining the SHG technique with the semiconductor laser technique is disclosed in JP-A-5-297428. According to the technique, a laser beam emitted from a semiconductor laser is made incident on an SHG element by a lens and converted into a second harmonic. In JP-A-5-297428 and the like, a structure of the SHG element is contrived to improve conversion efficiency.
However, in the technique in the past, although it is possible to improve characteristics of the SHG element, sufficient improvement of the conversion efficiency cannot be expected in the SHG element because of reasons (A) and (B) below.
(A) The lens provided between the semiconductor laser and the SHG element is a so-called field lens for condensing light. In the lens of this type, a distance to the SHG element is equal to or larger than a certain degree (longer than a focal length), a light beam density of the incident light on the SHG element falls. Since conversion energy of an optical wavelength conversion element substantially depends on the light beam density of the incident light, when the light beam density of the incident light falls, highly efficient wavelength conversion cannot be performed.
(B) In the field lens, since a radiation angle of a light beam has a large tilt with respect to an optical axis, the laser beam diffuses to the outside of the SHG element. This makes it difficult to effectively secure the inside of the SHG element as an optical path. Therefore, highly efficient wavelength conversion cannot be performed.